As is well known, fluid dynamic bearing devices have features in their high speed rotation, high rotational accuracy, quietness, and the like. Thus, the fluid dynamic bearing devices are suitably used as bearing devices for motors to be mounted to various electrical apparatus such as information apparatus, and more specifically, as bearing devices for spindle motors to be built in disk drives of HDDs and the like, for fan motors to be built in PCs and the like, or for polygon scanner motors to be built in laser beam printers (LBPs).
An example of the fluid dynamic bearing device is disclosed in Patent Literature 1. The fluid dynamic bearing device includes a housing having a bottomed cylindrical shape (cup shape), a bearing sleeve fixed to an inner periphery of the housing, a shaft member removably inserted along an inner periphery of the bearing sleeve, a radial bearing portion for supporting the shaft member in a radial direction by an oil film of lubricating oil formed in a radial bearing gap, a thrust bearing portion for supporting the shaft member in a thrust direction, a bottom gap having the thrust bearing portion received therein, and an annular member (sealing member) fixed to an inner periphery of an opening portion of the housing.
In the fluid dynamic bearing device, the annular member is fixed to the inner periphery of the opening portion of the housing in a state of engaging with the bearing sleeve in an axial direction (state of engaging with the bearing sleeve in a direction of removing the bearing sleeve). Accordingly, a force for fixing the bearing sleeve to the housing (force for removing the bearing sleeve) is increased, and thus relative positions of the housing and the bearing sleeve in the axial direction, and also desired bearing performance are maintained stably. Further, the fluid dynamic bearing device is used in a so-called fully-filled state in which an entire interior space of the housing is filled with the lubricating oil, and a sealing space (radial gap having a gap width larger than that of the radial bearing gap) is formed between an inner peripheral surface of the annular member and an outer peripheral surface of the shaft member. The sealing space is designed to function as a buffer for absorbing an amount of a volume change accompanied with a temperature change of the lubricating oil, thereby being capable of always maintaining an oil level of the lubricating oil in the sealing space within a range of the assumed temperature change. Therefore, reduction in bearing performance and contamination of peripheral environment, which result from leakage of the lubricating oil to an outside, can be prevented as much as possible.